1. Field of the Invention
This invention relates to an improved vehicle automatic transmission control system.
2. Description of the Prior Art
In both multi-step transmissions which control the gear ratio in a stepwise manner and continuously variable transmissions which control the gear ratio in a stepless manner, the prior art practice has generally been to determine the gear ratio by retrieval from a predetermined shift diagram stored in a microcomputer memory as a map, hereinafter referred to as "shift diagram map", using the vehicle speed and the throttle opening as address data.
Thus conventional automatic transmission control systems determine the gear ratio solely on the basis of vehicle speed and throttle opening and give no consideration to other operating parameters which should duly be taken into account. The result is that, unlike the gear changing operations of an experienced driver operating a vehicle with a manual transmission, the operations conducted by the prior art automatic transmission control systems do not match very well with the shift scheduling desired by the driver.
More specifically, since the prior art systems determine the gear ratio solely on the basis of the vehicle velocity and the throttle opening, they are unable to take into account other important operating parameters in determining the gear ratio, such as whether the vehicle is traveling up or down hill. Because of this, the gear ratio is frequently changed when driving in mountainous areas or the like, which irritates the driver because it differs from the shift scheduling that he or she wants and expects. Simply stated, it is extremely difficult to reflect the intentions of the driver in determining the gear ratio by the conventional control based on the shift diagram map.
Recent years have seen increasing use of fuzzy control in various fields. Since fuzzy control is well suited for use in expert systems designed to achieve control which reflects the operations and experience of an expert in the field concerned, it has also been applied to automatic transmission control systems, a number of which systems have been proposed by the present assignee. (See Japanese Laid-open Patent Publications No. 2(1990)-3739 and No. 2(1990)-85563 (also filed in the United States and matured as U.S. Pat. No. 5,036,730 and filed in EPO under 89306192.9); No. 2(1990)-3738 (also filed in the United States and matured as U.S. Pat. No. 5,079,705 and filed in EPO under 89306167.1); No. 2(1990)-138,558 and No. 2(1990)-138,561 (also filed in the United States and matured as U.S. Pat. No. 5,067,374 and filed in EPO under 89311976.8); No. 2(1990)-138,559, No. 2(1990)-138,560 and No. 2( 1990)-150,558 (also filed in the United States and matured as U.S. Pat. No. 5,079,704 and filed in EPO under 89311970.1); and No. 4(1992)-8964 (also filed in the United States under U.S. Pat. No. 691,066 and EPO under 91303878.2).
On the other hand, notwithstanding the drawbacks pointed out above, the more conventional technology for determining the gear ratio from the shift diagram map using the vehicle speed and the throttle opening as address data has the merit of being very well established.